Challenges of High Water Table.

High water table conditions make a spherical or hemispherical tank a preferred choice.

A 2000 gallon tank has a displacement of 20,000 pounds of water and requires that much downward weight to stop it from floating in high water conditions.

A conventional tank (rectangular) weighs more than a hemispherical tank but relies on its weight alone to combat buoyant forces from floating it up from the excavation. It is a common occurence for conventional concrete tanks to be floated up from high water table as they weigh less than the 20,000 pounds of water displacement.

The shape of the Turtle Tank is such that backfill acts as a force to hold the tank down.

The stabilizing downward force of backfill can be calculated by:

3'x 3' x 1/2 x 30' = 135 cubic feet of fill at 120 pounds per cu ft = 16,200 lb

plus the tank at 12,000 pounds equals a total downward force of 28,200 pounds leaving a net force of 8,200 pounds holding an empty tank from floating in a high water table.

Note: If you have concerns about pressure on a holding tank in a high water table area, there is a recommended procedure to keep pressure off the tank.